The present invention relates to telephone systems, and particularly to a line-powered pay telephone system. More specifically, this invention relates to a coin-operated customer owned telephone (COCOT) which, by its nature, does not rely upon signalling from the central office of the telephone company to provide call rating and coin collection information to the individual telephone instrument.
Pay telephones controlled by the central office of the telephone company are well-known in the art. Early pay telephones required operator intervention to give the caller information about the cost of a call and to determine whether the necessary money was inserted into the telephone. The operator could control the initiation and continuation of the call as well as send signals to the coin telephone to collect or refund the coins in the phone. Subsequent advances in the field have involved automation of the call rating and collection by computers associated with the central office. More recently, it has become legal for individuals to own and operate pay telephones (COCOTs) not owned by the telephone companies. In order for these phones to operate, the intelligence necessary to rate calls and control the collection of coins and the actual connection of the calls has to be controlled by computer circuitry within the telephone, rather than signals from the central office.
Also, prior art pay telephones generally required an independent power source supplied at the site of the telephone. However, line-powered telephones have been designed which enable the pay telephone to obtain the necessary operating power from the telephone line itself.
An example of a prior art line-powered telephone is that described in U.S. Pat. No. 4,759,054, to Regis B. Mellon. This patent describes a line-powered pay telephone which is connected to a coin trunk. The device disclosed in U.S. Pat. No. 4,759,054 relies upon the line current to power the system in both the on-hook and off-hook conditions. Because of its limitation to line current in the on-hook condition, since such current is limited by law to five microamperes, minimal circuitry can be powered by the line. Furthermore, since this instrument is connected to a coin trunk, it generally relies upon the central telephone office to provide the current to the coin collect relay in the off-hook condition, with a battery powered option for the coin collect in those situations where the central office current is not available to operate the coin collect relay. The battery described in the Mellon patent is not used in the on-hook condition and is only used to provide a high energy pulse to the escrow relay.
It is desirable to provide a line-powered coin telephone which is capable of being used as a COCOT, and not on the coin trunk. Such telephones are not able to use the telephone company's central office to provide escrow relay signals. Therefore, it is desirable for such a system to have the capability of internally generating coin escrow relay signals as needed. Batteries are not sufficiently reliable to ensure adequate current will be available each time a coin relay signal is required.
Furthermore, it is desirable to provide a line-powered COCOT which has the capability of being self-powered in the on-hook condition so that it has sufficient power necessary to maintain computer memory as well as to power-up the telephone to make calls during alarm conditions. The power provided by the line, alone, when the telephone is in the on-hook condition is not sufficient to provide these capabilities.